Spinal Stabilization System and Methods of Use

ABSTRACT

Devices and methods are adapted to permit fixation and stabilization of the bony elements of the skeleton. The devices permit adjustment and maintenance of the spatial relationship between neighboring bones. The motion between adjacent skeletal segments may be maintained, limited or completely eliminated.

REFERENCE TO PRIORITY DOCUMENTS

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/458,164, filed Aug. 12, 2014, which is a continuation ofU.S. patent application Ser. No. 12/790,754, filed May 28, 2010 and nowissued as U.S. Pat. No. 8,801,757. U.S. patent application Ser. No.12/790,754 is a continuation of U.S. patent application Ser. No.12/072,695, filed Feb. 26, 2008 and now issued as U.S. Pat. No.7,842,074. U.S. patent application Ser. No. 12/072,695 claims priorityof U.S. Provisional Patent Application Ser. No. 60/903,486 filed Feb.26, 2007 (expired), U.S. Provisional Patent Application Ser. No.60/921,570 filed Apr. 3, 2007 (expired), and U.S. Provisional PatentApplication Ser. No. 60/926,839 filed Apr. 30, 2007 (expired). Priorityof the aforementioned filing dates is hereby claimed and the disclosuresof the Applications are hereby incorporated by reference in theirentirety.

BACKGROUND

The present disclosure relates to devices and methods that permitfixation and stabilization of the bony elements of the skeleton. Thedevices permit adjustment and maintenance of the spatial relationship(s)between neighboring bones. Depending on the specifics of the embodimentdesign, the motion between adjacent skeletal segments may be maintained,limited or completely eliminated.

Spinal degeneration is an unavoidable consequence of aging and thedisability produced by the aging spine has emerged as a major healthproblem in the industrialized world. Alterations in the anatomicalalignment and physiologic motion that normally exists between adjacentspinal vertebrae can cause significant pain, deformity, weakness, andcatastrophic neurological dysfunction.

Surgical decompression of the neural tissues and immobilization of thevertebral bones is a common option for the treatment of spinal disease.In addition to mechanical fixation, a bone graft or comparablebone-forming material is used to connect the vertebral bones and, withossification of the graft material, the vertebral bodies are fusedtogether by the bony bridge. Currently, mechanical fixation is mostfrequently accomplished by anchoring bone screws into the pedicleportion of each vertebral body and then connecting the various screwfasteners with an interconnecting rod. The screw/rod construct producesrigid fixation of the attached bones.

The growing experience with spinal fusion has shed light on thelong-term consequences of vertebral immobilization. It is now acceptedthat fusion of a specific spinal level will increase the load on, andthe rate of degeneration of, the spinal segments immediately above andbelow the fused level. As the number of spinal fusion operations haveincreased, so have the number of patients who require extension of theirfusion to the adjacent, degenerating levels. The rigidity of the spinalfixation method has been shown to correlate with the rate of thedegenerative progression of the adjacent segments. In specific,implantation of stiffer instrumentation, such as rod/screw implants,produced a more rapid progression of the degeneration disease at theadjacent segment than use of a less stiff fixation implant.

An additional shortcoming of the traditional rod/screw implant is thelarge surgical dissection required to provide adequate exposure forinstrumentation placement. The size of the dissection site producesunintended damage to the muscle layers and otherwise healthy tissuesthat surround the diseased spine. A less invasive spinal fixationimplant would advantageously minimize the damage produced by thesurgical exposure of the spine.

Fixation of the spinous process segment of adjacent vertebrae provides aless rigid and less invasive method of vertebral fixation. Kapp et al.in U.S. Pat. No. 4,554,914 issued Nov. 26, 1985 disclosed a device oftwo elongated plates that are adapted to clamp onto adjacent spinousprocess. The plates are disadvantageously connected by locking boltsthat transverse the substances of each spinous process. Bolts placed inthis configuration will necessarily weaken the bony elements and lead tospinous process fractures and construct failure. Howland et al in U.S.Pat. No. 5,496,318, issued Mar. 5, 1996 disclosed the placement of aninter-spinous process spacer and encircling tension band to reducevertebral motion. While the device can reduce vertebral flexion andextension, it can not effectively resist vertebral movement in the othermotion planes. In U.S. Pat. No. 6,312,431 issued Nov. 6, 2001, Asforadisclosed a device comprised of two opposing plates that areinterconnected by a malleable tether and adapted to capture the adjacentspinous processes between them. As with the Howland device, the fixationstrength of this implant is limited by the mobile interconnectingtether. As such, neither implant can effectively immobilize thevertebral bones in all relevant motion planes. The lack of fixationsignificantly increases the possibility that the bone graft will notheal, the vertebral bones will not fuse, the construct will fail and thepatient will develop chronic pain.

Superior immobilization devices were disclosed by Robinson et al. inU.S. Pat. No. 7,048,736 issued May 23, 2006 and by Chin et al. in U.S.Pub. Nos. 2007/0179500, 2007/0233082 and 2007/0270840. Each of thesedocuments disclosed plates (or segments thereof) that engage each sideof two adjacent spinous processes, wherein the plates are interconnectedby a rigid member that resides within the interspinous space. Mechanicaltesting of the Robinson device was recently published by J C Wang et al.in the Journal of Neurosurgery Spine (2006 February; 4(2): 160-4) andthe text is hereby incorporated by reference in its entirety. The devicewas found to be weaker than conventional fixation techniques in allmodes of vertebral movement and particularly lacking in fixation ofrotational motion. Because of its limited stabilization properties, thedevice should be used in conjunction with additional implants. (See WangJ C et al. in the Journal of Neurosurgery Spine. 2006 February; 4(2):132-6. The text is hereby incorporated by reference in its entirety.]

As an additional shortcoming, the Robinson device can not be used tofixate the L5 vertebral bone to the sacrum. The spinous process of thefirst sacral vertebra is simply too small to permit adequate bonepurchase and fixation with either the Robinson or Chin device. Since theL5/S1 level is a frequent site of spinal disease, the inapplicability ofthese devices at this level is a significant limitation of theseimplants.

In U.S. Pub. Nos. 2006/0036246, Carl and Sachs disclose a fixationdevice adapted to fixate the spinous process of one vertebral level tobone screws anchored into the pedicle portion of an adjacent vertebrallevel. While this invention would permit application at the L5/S1 leveland circumvent one disadvantage of the aforementioned spinous processfixation plates, it relies on direct screw fixation into the distalaspect of the spinous process. This technique disadvantageouslyreplicates the inadequate fixation characteristics of the Kapp devicepreviously discussed (U.S. Pat. No. 4,554,914) and carries a highlikelihood of spinous process fracture and complete construct failure.Indeed, the inventors try to address this design flaw by augmenting thestrength of the spinous process through the use of an internal bonefiller or an external brace. Regardless of these efforts, however, thedisclosed device provides a cumbersome implant that carries a highlikelihood of spinous process fracture and complete loss of vertebralfixation.

SUMMARY

The preceding discussion illustrates a continued need in the art for thedevelopment of a spinous process device and method that would providesuperior vertebral fixation than existing spinous process implants. Thedevice should be amenable to placement through a minimally invasivesurgical approach. When vertebral fusion is desired, the devicedesirably provides adequate fixation in all movement planes so that theprobability of bone graft healing is maximized. The implant woulddesirably provide less rigid fixation than traditional rod/screwfixation.

In the treatment of spinal disease, it is sometimes desirable to limitvertebral motion in one or more axis while maintaining movement in othermotion planes. Vertebral segments that are treated using these motionpreservation techniques will not be fused and a bone graft spanning thespace between the vertebral bones is not employed. When motionpreservation is desired, the device provides adequate fixation onto eachattached vertebral bone while controlling the motion between them.Moreover, a hybrid device would advantageously provide fusion at one ormore vertebral levels and motion preservation at other vertebral levels.

This application discloses novel implants and methods of implantationthat address current deficiencies in the art. In an embodiment, there isdisclosed an orthopedic device adapted to fixate the spinous processesof one vertebral bone to bone fasteners anchored into the pedicleportion of an adjacent vertebral body. The implant may capture thespinous process by using an encircling contoured rod or hooks.Alternatively, the implant may contain at least one barbed boneengagement member located on each side of the spinous process andadapted to forcibly abut and fixate into the side of the spinousprocess. The device further contains a locking mechanism that is adaptedto transition from a first unlocked state wherein the device componentsare freely movable relative to one another to a second locked statewherein the device is rigidly immobilized and affixed to the bone.

Alternative embodiments of the aforementioned device are disclosed. Inone embodiment, the device is adapted to fixate at least three vertebralbones. In that embodiment, the device captures the spinous processes ofone vertebral bone and fixates it onto an elongated rod that is adaptedto engage bone fasteners anchored into the pedicle portion of at leasttwo additional vertebral bodies. In another embodiment, the device isadapted to attach onto the rod portion of an existing screw/rodconstruct and functions to extend the level of vertebral fixation.

In other embodiments, there is disclosed a series of orthopedic devicesthat are adapted to fixate onto the spinous processes of one vertebralbone and onto bone fasteners anchored into the pedicle portion of anadjacent vertebral body. The device provides controlled movement betweenthe two attached vertebral bones. Multiple iterations of this device areillustrated. In some embodiments, bone graft or bone graft substitutemay be used to fixate and fuse the device onto each of the anchoredvertebral bones while still permitting movement between them.

In an alternative embodiment, the device also contains an elongated rodthat is adapted to engage bone fasteners anchored into the pedicleportion of at least two additional vertebral bodies. This design featureproduces a hybrid device that provides controlled motion between atleast a first pair of vertebral bones and rigid immobilization betweenat least a second pair of vertebral bones.

In an additional embodiment, a implant is used to fixate onto thespinous process of each of two adjacent vertebral bone. The implantcontains at least one barbed bone engagement member located on each sideof the spinous process and adapted to forcibly abut and fixate into theside of the spinous process at each level. The implant allows controlledmovement between the two attached spinous processes. The implant mayfurther contain a cavity adapted to accept a bone graft or bone graftsubstitute so that, with bone formation, the device members may fuseonto the spinous processes and provide superior device adhesion to thevertebral bone. In another embodiment, a bone containment device isdisclosed that is adapted to span the distance between the lamina ofneighboring vertebrae. The device contains an internal cavity adapted toaccept a bone graft or a bone graft substitute so that, with boneformation, the lamina of neighboring vertebral bones are fused together.

In one aspect, there is disclosed an orthopedic device adapted to fixateat least two vertebral bones, comprising: at least one bone engagementmember located on each side of a spinous process of a first vertebrawherein the bone engagement member are each forcibly compressed andaffixed onto the sides of the spinous process; a connector memberadapted to interconnect each bone engagement members on one side of aspinous processes of a first vertebra with at least one bone fasteneraffixed to a second vertebra; a cross member extending across thevertebral midline and adapted to adjustably couple the bone engagementmember and connector member on one side of the vertebral midline withthe bone engagement member and the connector member on the other side ofthe vertebral midline; and a connection between the bone engagementmembers the connection comprising a connector member, and a cross memberwherein the connection is capable of reversibly transitioning between afirst state where the orientation between the bone engagement member,the connector member and the cross member is changeable in at least oneplane and a second state where the orientation between the boneengagement member, the connector member and the cross member is rigidlyaffixed.

In another aspect, there is disclosed an orthopedic device adapted tofixate at least two vertebral bones, comprising: at least one boneengagement member located on each side of a spinous process of a firstvertebra wherein the bone engagement member is forcibly compressed andaffixed onto the sides of the spinous process; a connector memberadapted to inter-connect each bone engagement members on one side of aspinous processes of a first vertebra with at least one rod that is usedto inter-connect at least two bone fastener affixed to additionalvertebral bones; a cross member extending across the vertebral midlineand adapted to adjustably couple the bone engagement member andconnector member on one side of the vertebral midline with the boneengagement member and connector member on the other side of thevertebral midline; and a connection between a bone engagement members,the connection comprising a connector member and a cross member whereinthe connection is capable of reversibly transitioning between a firststate where the orientation between the engagement member, the connectormember and the cross member is changeable in at least one plane and asecond state where the orientation between the engagement member, theconnector member and the cross member is rigidly affixed.

In another aspect, there is disclosed an orthopedic device adapted tofixate at least two vertebral bones, comprising: at least one contouredrod that contacts at least one surface of the spinous process of a firstvertebra; a connector member adapted to interconnect one end of thecontoured rod that is located on one side of a spinous processes of afirst vertebra with a bone fastener affixed to a second vertebra; and adevice body member extending across the vertebral midline and adapted toadjustably couple at least one end of the contoured rod with theconnector members wherein the device body member further contains atleast one locking mechanism that is capable of reversibly transitioningbetween a first state wherein the orientation between the contoured rodand at least one connector member is changeable in at least one planeand a second state wherein the orientation between the contoured rod andat least one connector member is rigidly affixed.

In another aspect, there is disclosed an orthopedic device adapted tofixate at least two vertebral bones, comprising: at least one hookmember that contacts at least one surface of the posterior aspect of afirst vertebra; and a connector member adapted to interconnect one endof the hook member attached to the posterior aspect of a first vertebrawith a bone fastener affixed to a second vertebra; a device body memberextending across the vertebral midline and adapted to adjustably coupleat least one hook member attached to the posterior aspect of a firstvertebra the connector members wherein the device body member furthercontains at least one locking mechanism that is capable of reversiblytransitioning between a first state wherein the orientation between thehook member and at least one connector member is changeable in at leastone plane and a second state wherein the orientation between the hookmember and at least one connector member is rigidly affixed.

In another aspect, there is disclosed an orthopedic device adapted tocontrol motion between at least two vertebral bones, comprising: atleast one bone engagement member located on each side of a spinousprocess of a first vertebra wherein the bone engagement member isforcibly compressed and affixed onto the sides of the spinous process; aconnector member adapted to interconnect each bone engagement members onone side of a spinous processes of a first vertebra with at least onebone fastener affixed to a second vertebra, wherein the engagementmember contains a channel adapted to accept an end of the connectormember and wherein the motion permitted by the interaction of each ofthe two channel and connector member surfaces determines the motionprofile permitted by the device; a cross member extending across thevertebral midline and adapted to adjustably couple bone engagementmember and connector member on one side of the vertebral midline withthe bone engagement member and connector member on the other side of thevertebral midline; and a connection between the bone engagement membersand cross member wherein the connection is capable of reversiblytransitioning between a first state where the orientation between theengagement member and the cross member is changeable in at least oneplane and a second state where the orientation between the engagementmembers and the cross member is rigidly affixed.

Other features and advantages will be apparent from the followingdescription of various embodiments, which illustrate, by way of example,the principles of the disclosed devices and methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows perspective views of an orthopedic implant adapted tofixate the spinous process of a first vertebral bone to screw fastenersaffixed to the pedicle portion of a second vertebral bone.

FIG. 2 illustrates multiple views of the implant.

FIG. 3 shows an exploded view of the implant.

FIG. 4 shows a section view through the locking mechanism of theimplant.

FIG. 5 shows a perspective view of the implant attached onto a segmentof the spine.

FIGS. 6 and 7 illustrate multiple views of a second device embodiment.

FIG. 8 shows a partly exploded view of the second device embodiment.

FIGS. 9 and 10 illustrate multiple views of another device embodiment.

FIG. 11 illustrates a perspective view of a preferred embodiment of thecurrent invention.

FIG. 12 shows the device of FIG. 11 in multiple orthogonal planes.

FIG. 13 shows an exploded view of the implant.

FIGS. 14 and 15 illustrate cross-sectional views of the lockingmechanism of the implant.

FIGS. 16 through 18 illustrate devices and methods for vertebraldistraction in preparation for device placement.

FIG. 19 shows a method of vertebral and nerve decompression.

FIGS. 20a-20c show the device of FIG. 11 attached to the spine.

FIG. 21 illustrates the addition of a second device at an adjacentspinal level.

FIG. 22 shows an additional device embodiment that is adapted to fixatemultiple vertebral levels.

FIG. 23 shows a perspective view of an alternative embodiment of thedevice shown in FIG. 11.

FIG. 24 shows the device of FIG. 23 in multiple orthogonal planes.

FIG. 25A shows the device of FIG. 23 attached to a spine model.

FIG. 25B illustrates a cross-sectional view wherein the spinous processfixation screw is shown.

FIG. 26A shows another embodiment of the device of FIG. 11 wherein therods are replaced with paddle attachment members.

FIG. 26B shows an exemplary embodiment of a paddle attachment member.

FIGS. 27 and 28 illustrate additional device embodiments.

FIG. 29 shows another device embodiment used to fixate three or morevertebral bones.

FIG. 30 shows the device of FIG. 29 attached to the spine.

FIGS. 31 to 33 illustrate a device adapted to attach onto existingrod/screw instrumentation.

FIG. 34 shows a perspective view of a device embodiment adapted topreserve motion between the vertebral bodies.

FIG. 35 shows the device of FIG. 34 in multiple orthogonal planes.

FIG. 36 illustrates an exploded view.

FIG. 37A shows a cross-sectional view through the articulationmechanism.

FIG. 37B shows a cross-sectional view through the locking mechanism.

FIG. 38 illustrates a perspective view of an additional deviceembodiment.

FIG. 39 shows the device of FIG. 38 in multiple orthogonal planes.

FIG. 40 illustrates an exploded view.

FIGS. 41, 42 and 43 illustrate cross-sectional views at different pointswithin the device.

FIG. 44 shows a perspective view of an alternate embodiment of themotion preservation device.

FIG. 45 illustrates a perspective view of an additional deviceembodiment.

FIG. 46 shows the device of FIG. 45 in multiple orthogonal planes.

FIG. 47 illustrates an exploded view.

FIG. 48 shows a cross-sectional view through the locking mechanism.

FIG. 49 illustrates a perspective view of an alternative embodiment.

FIG. 50 shows an exploded view of the device of FIG. 49.

FIG. 51 shows an alternative embodiment of the device in FIG. 49.

FIGS. 52 and 53 illustrate additional device embodiments.

FIG. 54 illustrates another device embodiment.

FIG. 55 shows the device of FIG. 54 in multiple orthogonal planes.

FIG. 56 shows an exploded view.

FIG. 57 illustrates an additional device embodiment.

FIG. 58 shows exploded views of the device.

FIG. 59 shows a sectional view through the locking mechanism andarticulation surface.

FIG. 60A shows the posterior aspect of a spine.

FIG. 60B shows a bone containment implant in place at the L4/5 level.

FIG. 61A shows a perspective view of a bone containment implant.

FIG. 61B illustrates the device of FIG. 61A in multiple orthogonalviews.

FIG. 62 shows another embodiment of the bone containment implant inplace at the L4/5 level.

DETAILED DESCRIPTION

FIGS. 1-3 show various views of an orthopedic device adapted to fixatethe spinous process of a first vertebral bone to screw fasteners affixedto the pedicle portion of a second vertebral bone. The device includes acentral member 110 having a pair of movably attached rods 115 extendingoutwardly therefrom. A central threaded bore 112 is contained in member110 and serves as an attachment point for the device placementinstruments. Each of the rods 115 has a ball-shaped head that ispositioned inside a complimentary shaped seat inside the central member110. The spherical head is positioned into the seat inside member 110and retained in place by collapsible “C” ring 116. In the unlockedstate, the spherical head of rod 115 is freely movable within the seatof member 110.

A U-shaped rod 120 is also attached to the central member 110. The rod120 can be fixated to the central member 110 by tightening a pair oflock nuts 125 downwardly onto ends of the rod 120. As shown in FIG. 2,the lock nuts 125 are positioned atop the heads of the rods 115. Thispermits the lock nuts 125 to provide a downward force onto both theU-shaped rod 120 and the heads of the rods 115. In this manner, the locknuts 125 serve as a locking member that simultaneously locks theLi-shaped rod 120 and the rods 115 to the central member 110. TheLi-shaped rod 120 is adapted to fit around a spinous process of avertebral bone. The rod 120 can have various shapes and configurationsbeside a U-shape that permits the rod to be fit around a spinousprocess.

FIG. 3 shows an exploded view of the device and FIG. 4 shows across-sectional view of the device through the locking mechanism. Alocking plug 305 is interposed between each of rods 120 and thespherical heads of rods 115. As the locking nuts 125 are tighteneddownward onto the rod 120, the locking plugs 305 are advanced onto thespherical heads of rods 115, locking and immobilizing the rods 115relative to the central member 110.

FIG. 5 shows a perspective view of the device attached onto a segment ofthe spine. The vertebrae are represented schematically and those skilledin the art will appreciate that actual vertebral bones may includeanatomical details that differ from those shown in FIG. 5. The U-shapedrod 120 is shaped such that it can wrap around or otherwise secure ontothe spinous process of a vertebral body. The central member 110 is alsopositioned to contact the spinous process. The foot plate 118 of member110 is preferably positioned beneath the lamina of the upper vertebralbone. The U-shaped rod 120 can be adjusted relative to the centralmember 110 prior to the actuation of the lock nuts. The rod 120 canadjustably slide relative to the central member 110 to accommodatespinous processes of various sizes. Preferably, the rod 120 ispositioned around the spinous process in a manner that tightly capturesthe top surface of the spinous process against the central rod bend andthe bottom surface of the spinous process or lamina against member 110.After appropriate positioning of rod 120, the free end of each rod 115is rotated and placed into the rod-receiving seat of the previouslyplaced bone fasteners 122. The fastener lock nuts are tightened and theends of rods 115 are immobilized relative to the fasteners.Subsequently, tightening of lock nuts 125 immobilizes rod 122, rods 115and central member 110 relative to one another and produce a rigidimplant. As illustrated, the device fixates the spinous processes of afirst vertebral bone to bone fasteners anchored into the pedicle portionof a second vertebral bone.

FIGS. 6 and 7 show another device embodiment. An exploded view is shownin FIG. 8. While similar to the previous embodiment, the current deviceuses rods 120 with terminal hooks 805 to attach onto the upper aspect ofthe spinous process or upper edge of the lamina of the upper vertebralbone. As shown in the exploded view of FIG. 8, the end 805 of each rod120 is configured as a hook wherein the two hooks 805 a and 805 b caninterfit with one another. The cylindrical end of each rod 120 isadapted to fit within complimentary bores 126 of member 110.

As in the previous embodiment, central member 110 has a cavity adaptedto accept the spherical head of each rod member 115. “C” ring 116retains the spherical heads attached to member 110 after deviceassembly. The locking mechanism of the device is similar to that of theprevious embodiment.

Advancement of lock nuts 125 immobilizes rods 120, rods 115 and centralmember 110 relative to one another. The placement protocol is similar tothat of the previous embodiment. However, as noted, hook member 805 maybe alternatively attached onto the superior edge of the lamina of theupper vertebral bone.

FIGS. 9 and 10 illustrate multiple views of another device embodimentthat fixates the spinous processes of one vertebral bone to bonefasteners anchored into the pedicle portion of an adjacent vertebralbody. The vertebrae are represented schematically and those skilled inthe art will appreciate that actual vertebral bones may includeanatomical details that differ from those shown in these figures. Inthis embodiment, a U-shaped rod 120 is sized and shaped to wrap aroundthe spinous process of a first vertebral body. Opposed ends of the rod120 are coupled to bone fasteners such as bone screw assemblies 810. Thebone fasteners are attached to the pedicles of an adjacent vertebralbody. Unlike the previous embodiments, this device does not include acentral member.

FIGS. 11-13 show another embodiment of a device that fixates the spinousprocesses of one vertebral body to bone fasteners anchored into thepedicle portion of an adjacent vertebral body. The device includes apair of central members 1105 a and 1105 b (collectively central members1105) with opposed interior surfaces. Fixation members such as barbs1107 are positioned on the interior surfaces such that the barbs faceinward for attaching to a spinous process positioned between the centralmembers 1105. The central members 1105 are slidably mounted on a rod1110 such that the central members 1105 can move toward and away fromone another. In this manner, the size of the space between the centralmembers 1105 can be adjusted to accommodate spinous processes of varioussizes. Further, the orientation of members 1105 relative rod 1110 isadjustable in multiple planes.

Each rod 115 is coupled to a central member 1105 such that it extendsoutwardly therefrom. Rod 115 has a spherical head that is positionedinside a complimentary shaped seat inside a respective central member1105 and retained in position collapsible “C” ring 116. In the unlockedstate, the spherical head of rod 115 is freely movable within member1105 in a ball and socket manner. The end of each rod 115 can beattached to a bone fastener, such as pedicle screw assemblies 810, thatis anchored to the pedicle portion of a vertebral bone.

The top surface of each member 1105 contains a bore 1127, which extendsfrom the top surface to the cavity adapted to receive the spherical headof rod 115. The upper aspect of bore 1127 is threaded. Bore 1127 iscrossed by bore 1129, wherein the latter bore extends from the lateralto the medial wall of member 1105. A cross sectional view through thelocking mechanism is shown in FIGS. 14 and 15. Spherical member 1410 hascentral bore 1412 and full thickness side cut 1414, thereby forming acompressible “C” ring that can be compressed onto the contents of bore1412. In the assembled device, rod 1110 is positioned within centralbore 1412 and can translate relative to it. With the application of acompressive load onto the outer surface of member 1410 by threadedlocking nut 1125, member 1410 is compressed onto rod 1110 and the latteris immobilized within bore 1412. Retention pins 1145 are used to retainrod 1110 within member 1410 in the assembled device.

Advancement of each of lock nuts 1125 immobilizes rod 1110, rod 115 andcentral member 1105 relative to one another and renders the devicerigid. With reference to the cross-sectional views of FIGS. 14 and 15,tightening lock nut 1125 downwardly onto spherical member 1410 producesa compressive load onto rod 1110 and a downward force onto locking plug1405. The latter is pushed towards the spherical head of rod 115,thereby immobilizing rod 115 within central members 1105. In thismanner, advancement of each lock nut 125 provides a downward force ontoboth rod 1110 and the spherical head of rod 115 contained with eachmember 1105. Thus, each lock nut 125 serves as a locking member thatsimultaneously locks rod 1110 and rod 115 to the central member 1105.

The spinal level to be implanted has an upper and a lower vertebral boneand the device is attached onto the posterior aspect of these vertebralbones. Prior to device placement, the upper and lower vertebral bonesare distracted to facilitate decompression of the nerve elements. FIG.16 shows a perspective, assembled view of a distractor device. Forclarity of illustration, the vertebral bodies are representedschematically and those skilled in the art will appreciate that actualvertebral bodies include anatomical details not shown in FIG. 16. Thedevice generally includes a pair of anchors that include elongatedistraction screws 1610 coupled to a platform 1615. Each of thedistraction screws 1610 is advanced into the posterior surface of aspinous process and follows a posterior to anterior trajectory along thelong axis of the spinous process. The distal end of each screw includesa structure for attaching to the spinous process, such as a threadedshank. The proximal ends of the distraction screws 1610 are attached tothe platform 1615. The screws 1610 are axially positioned within sheaths1619 that surround the screws and extend downwardly from the platform1615.

The distraction actuator 1622 is actuated to cause one of thedistraction screws to slide along the rail 1621 such that it moves awayfrom the other distraction screw. This applies a distraction force tothe vertebral bodies to distract the vertebral bodies—as shown in FIG.17. (In another embodiment, shown in FIG. 18, the distraction screws arereplaced by clip members 1805 that couple to the spinous processes orlamina of the vertebral bodies. Other known methods of vertebraldistraction may be alternatively used.) The decompression of the nerveelements is performed under distraction and it is schematicallyillustrated in FIG. 19. The bony and ligament structures that arecompressing the nerves are removed from the lower aspect of the laminaof the upper vertebra and the upper aspect of the lamina of the lowervertebra (regions 1152).

Prior to device implantation, bone fasteners 810 had been placed intothe pedicel portion of the lower vertebra on each side of the midline. Abone graft or bone graft substitute is packed with the facet joints andused to span the distance between the lamina of each of the upper andlower vertebra. The implant is positioned at the level of implantationsuch that opposing central members 1105 are disposed on either side of aspinous process of a the upper vertebral body. A compression device (notshown) attaches onto the lateral wall of each opposing central member1105 at indentation 11055. The compression device forcefully abuts themedial aspect of each central member 1105 against a lateral wall of thespinous process and drives spikes 1107 into the bone. Spikes 1107provide points of device fixation onto the each side of the spinousprocesses.

With the compression device still providing a compressive force, thedistal ends of rods 115 are positioned into the rod receiving portionsof bone fasteners 810. The locking nuts of the fasteners are actuated sothat each rod 115 is locked within the respective fastener. Lock nuts1125 are actuated, locking the device's locking mechanism and immobilizeopposing central members 1105, the interconnecting rod 1110 and rods 115relative to one another. The compression device is removed, leaving thedevice rigidly attached to the upper and lower vertebral bones.

FIGS. 20a-20c show the device of FIG. 11 attached to the spine. Asmentioned, the central members 1105 are spaced apart with a spinousprocess of an upper vertebra positioned in the space between them. Therods 115 are oriented so that they extend toward respective bonefasteners that are anchored to the pedicle portion of a lower vertebra.In this manner, the device fixates the spinous processes of onevertebral body to bone fasteners anchored into the pedicle portion of anadjacent vertebral body. FIG. 21 illustrates the addition of a seconddevice at an adjacent spinal level. Note that device can be used tofixate the L5 vertebra to the sacrum.

FIG. 22 shows another embodiment of a device that is similar to thedevice of FIG. 11. In this embodiment, the rods 115 have a length thatis sufficient to span across multiple vertebral levels. This permits thedevice to be used to fixate multiple vertebral bodies across multiplelevels to a spinous process of a single vertebral body.

FIGS. 23 and 24 show an alternative embodiment. In this device, at leastone of the central members 1105 has a portion 2305 that extendsoutwardly and overhangs the space between the central members 1105. Theportion 2305 is sized, shaped, and contoured such that it can fit aroundthe spinous process that is positioned between the central members 1105.A bore 2310 extends through the portion 2305. The bore receives a bonefastener, such as a bone screw, that can be driven into the posteriorsurface of the spinous process and having a posterior to anteriortrajectory that substantially follows the long axis of the spinousprocess. FIG. 25A shows the device of FIG. 23 attached to a spine model.FIG. 258 illustrates a cross-sectional view wherein the spinous processfixation screw 2510 is shown extending through the portion 2305 and intothe spinous process.

FIG. 26A shows another embodiment of the device of FIG. 11 wherein rods115 are replaced with paddle attachment members 2605. FIG. 268 shows anexemplary embodiment of a paddle attachment member 2605. The paddleattachment member 2605 is used in place of a rod 115. The attachmentmember 2605 has a head that fits into the central member 1105 and alsohas an opening 2610 that can be coupled to a bone fastener, such as apedicle screw assembly.

FIGS. 27 and 28 show additional embodiments of the device of FIG. 11. Inthese devices, a portion 2705 is sized and shaped to capture theinferior surface of the lamina of the upper vertebral bone. In theembodiment of

FIG. 27, the portion 2705 extends outward from the rod 1110. In theembodiment of FIG. 28, the portion 2705 extends outward from each of thecentral members 1105.

FIG. 29 shows another device embodiment used to fixate three or morevertebral bones. In this embodiment, the central members 1105 aresufficiently long such that the spinous processes of one or morevertebral bodies can fit between the central members 1105. The centralmembers 1105 have barbs or other attachment means that are adapted tosecure to the spinous processes. One end of each of the central membershas a rod 115 movably attached thereto while the opposed end has anotherrod 117 movably attached thereto. The rods 115 and 117 can extendoutward at any of a variety of orientations and angles relative to thecentral members. The rods 115 and 117 can be attached to pedicle screwassemblies for attaching the device to adjacent vertebral bodies. Thus,the device is adapted to fixate the spinous process of a middle vertebrato screw fasteners attached to the pedicle portions of an upper and alower vertebra. FIG. 30 shows the device of FIG. 29 attached to aschematic representation of the spine.

FIGS. 31 to 33 illustrate a device adapted to attach onto existingrod/screw instrumentation and extend the fusion to a additional level.Each of two rods 3110 is attached to a pair of vertebral bodies in aconventional screw/rod fixation arrangement. Each rod 3110 is attachedto two pedicle screw assemblies 3115—as shown in FIG. 31. The extensiondevice has a pair of central members 1105 that are positioned on opposedsides of a spinous process of an upper vertebra. Rods 115 extendoutwardly from the device. The rods 115 movably attach to the rods 3110via a pair of brackets 3120. Perspective views of bracket 3120 are shownin FIG. 33. Each bracket is sized to receive a spherical end of rod 115while also receiving a cylindrical segment of rod 3110. Actuation of thelocking screw 3130 of bracket leads to the upward movement of member3150 and the immobilization of rod 3110 and the special head of rod 115within bracket 3120. A cross-sectional view of the locking mechanism isshown in FIG. 32.

FIG. 34 illustrates a device embodiment 605 adapted to fixate onto thespinous processes of one vertebral bone and bone fasteners anchored intothe pedicle portion of an adjacent vertebral body. The device providescontrolled movement between the two attached vertebral bones. FIG. 35shows the device in multiple orthogonal planes and FIG. 36 shows thedevice components in an exploded view. Each of opposing body members 612has a top surface, bottom surface, an outer side surface, an inner sidesurface and a front and back surface. Each medial surface contains spikeprotrusions 617 that are adapted to be driven into the side surface of aspinous process and serve to increase device fixation onto bone. Thelateral surface contains opening 622 of channel 624 that is intended toreceive the spherical head 632 of rod 634.

Movement of head 632 within channel 624 forms the mobile bearing surfaceof the implant. A cross-sectional view of head 632 contained withinchannel 624 is illustrated in FIG. 37A. As shown, head 632 can moveunopposed within channel 624. In an alternative embodiment, a springmember is placed within channel 624 so that the position of head 632 isbiased against movement away from a default position. Preferably, in thedefault position, head 632 is positioned at the end of channel 624 thatis adjacent to bore 628—as shown in FIG. 34.

The top surface of each body member 612 contains bore 628 adapted toaccept a bone fastener 629. Preferably, but not necessarily, bores 628of the opposing body members 612 are angled in one or more planes sothat the seated bone fasteners are not parallel. Non-parallel boretrajectories provide a crossed screw configuration and increasedresistance to screw pull-out. As previously discussed, the seated screwsmay engage any portion of the lamina or spinous process bone but arepreferably targeted and placed to engage the junction of the lamina andspinous process.

The top surface of each body member 612 contains a cavity 636 with fullthickness bore holes 638 within the medial cavity wall. The cavity isadapted to accept a segment of bone graft or bone graft substitute andto function as a bone containment cage. With time, the graft materialwithin cavity 636 of an implanted device 605 will fuse with the lateralwall of the spinous process and provide an additional attachment pointwith the underlying bone. Since it contains living bone tissue,ossification of the fusion mass will provide a stronger and moreenduring bridge between the implant and vertebral bone than anymechanical fastener.

The top surface of each body member 612 contains a second bore 642,wherein partial thickness bore 642 does not extend through to the bottomsurface of the body member. The upper aspect of bore 642 is threaded.Bore 642 is crossed by bore 646, wherein the full thickness bore 646extends from the lateral to the medial wall of body member 612. Bores642 and 646 contain the device's locking mechanism. (A cross sectionalview through the locking mechanism is shown in FIG. 37B.) Sphericalmember 652 has central bore 654 and full thickness side cut 655, therebyforming a compressible “C” ring that can be compressed onto the contentsof bore 654. In the assembled device, longitudinal member 658 ispositioned within central bore 654 and can translate relative to it.With the application of a compressive load onto the outer surface ofmember 652 by threaded locking nut 656, spherical member 652 iscompressed onto longitudinal member 658 and the latter is immobilizedwithin bore 654. Retention pins 645 are used to retain longitudinalmember 658 in the assembled device. In the assembled configuration,retention pins 647 are positioned within side cut 655 of sphericalmember 652 so as to limit the extent of rotation of opposing bodymembers 612.

The spinal level to be implanted has an upper and a lower vertebral boneand the device is attached onto the posterior aspect of the vertebralbones. Prior to device placement, bone fasteners 660 had been placedinto the pedicel portion of the lower vertebra on each side of themidline. In addition, each side of the spinous process of the uppervertebra is gently decorticated in order to maximize the likelihood ofbone (fusion) mass formation. Each of opposing body members 612 isplaced on an opposite side of the spinous process of the upper vertebra.A compression device (not shown) is used to compress each body member612 onto a side of the spinous process and drive the spike protrusions617 into the bone surface. With the compression device still providing acompressive force, the distal ends of rods 634 are positioned into therod receiving portions of bone fasteners 660. Preferably, each head 632is positioned at the end of channel 624 immediately adjacent to bore 628prior to locking bone fasteners 660 onto rods 634. This configurationassures that vertebral extension is limited to the position set at thetime of surgery. The locking nuts of the fasteners are then actuated sothat each rod 634 is locked within the respective fastener 660. Lockingnuts 656 of device 605 are then actuated, locking the device's lockingmechanism and immobilize opposing body member 612 and theinterconnecting longitudinal member 658 relative to one another. Thecompression device is removed, leaving the device rigidly attached tothe upper and lower vertebral bones. Preferably, but not necessarily,cavity 636 is packed with bone graft or bone graft substitute so that,with time, a bone fusion mass connects the device to the side wall ofthe spinous process. If desired, a bone fastener 629 can be placedthrough each bore hole 628 into the underlying bone and further increasedevice fixation onto bone.

It is important to note that spike protrusions 617 and fastener 629provide immediate device fixation to the upper vertebral level. Withtime, these fixation points may weaken from the cyclical device loadingthat invariably results during routine patient movement. Formation andossification of the bone fusion mass contained within cavity 636provides long-term fixation for the device. In contrast to spike andscrew fixation, the fusion mass will increase in strength with time andprovide a more permanent attachment point for the device. In this way,the immediate fixation of the spike and fasteners and the long-termfixation of the fusion mass compliment one another and provide optimalfixation for the device.

After device implantation, certain movements between the upper and thelower vertebras are permitted while other movements are limited. Forexample, the illustrated embodiment permits forward flexion of the uppervertebra relative to the lower vertebra. However, extension is limitedby the position set at the time of implantation (that is, the positionof head 632 within channel 624). Anterior translation of the uppervertebral bone relative to the lower vertebral bone is significantlylimited so that aberrant motion resulting in spondylolisthsis isprevented. Lateral flexion between the vertebral bones is permitted butto a lesser degree than that of normal physiological vertebral motion.Vertebral rotation is substantially eliminated.

These limitations are determined by the interaction of heads 632 withchannels 624 and can be varied by the shape and/or orientation of one orboth of these structures. For example, extending the diameter of channel624 in a medial to lateral direction will permit an increase invertebral rotation. Further, a channel with lesser medial to lateraldiameter at one end and a greater medial to lateral diameter at anotherend will permit a variable degree of rotational movement, wherein theextent of rotation depends of the extend of anterior flexion. Thisconfiguration can simulate physiological vertebral motion, whereingrater vertebral rotation is permitted in anterior flexion than inextension. As can be easily seen, numerous alternative motioncharacteristics can be produced by one of ordinary skill in the artthrough the simple manipulation of the shape and/or orientation of heads632 and/or channels 624. In addition, malleable members can be placedwithin channel 624 so that the position of head 632 is biased towards adefault position and movement away from that position is opposed.

An alternative embodiment is shown in FIG. 38. While similar to thepreceding embodiment, this device provides a cross-member thatinter-connects the bone fasteners 660 so as to obviate the possibilityof fastener rotation (along its long axis) within the pedicle portion ofthe bone. The cross member also increases the resistance to fastenerpull-out from the lower vertebral bone. FIG. 39 shows the device inmultiple orthogonal planes. An exploded view is shown in FIG. 40 andmultiple cross-sectional views are shown in FIGS. 41, 42 and 43.

Device 685 is adapted to fixate onto the spinous processes of onevertebral bone and bone fasteners anchored into the pedicle portion ofan adjacent vertebral body. As before, each of opposing body members 612has side spikes 617, a central cavity 636 adapted to accept a boneforming graft, and a locking mechanism adapted to immobilize bodymembers 612 to interconnecting longitudinal member 658. (A section viewthrough the locking mechanism is shown in FIG. 41.) The top surface ofeach body member 612 contains bore 628 adapted to accept a bone fastener629. Side indentations 662 receive the compression device during deviceimplantation.

The inferior surface of each body 612 contains opening 682 of channel686. Head 692 of rod 690 travels within channel 686 and forms the mobilebearing surface of the implant. Retention pin 681 (FIG. 40) is used toretain head 692 within channel 682 and prevent device disassembly. Asbefore the motion characteristics permitted by the implant aredetermined by the interaction of heads 692 with channels 686 and can bevaried by the shape and/or orientation of one or both of thesestructures. (A section view through the bearing surface is shown in FIG.42.) Examples of the possible configuration changes were previouslydiscussed. In addition, malleable members can be placed within channel682 so that the position of head 692 is biased towards a defaultposition and movement away from that position is opposed.

Interconnecting rod 702 is used to attach the device onto the bonefasteners imbedded within the pedicel portion of the lower vertebralbody. Rod 702 is comprised of telescoping segments 704 and 706 so thatthe rod length may be varied. Segment 704 contains rectangularprotrusion 704 that, in the assembled state, is housed with acomplimentary bore within segment 706. A cross-sectional view throughrod 702 is shown in FIG. 43. A side rod 690 with head 692 (bearingsurface) is contained in each of segments 704 and 706—as illustrated.The procedure for placement of device 685 is similar to the placementprocedure previously described for device 605.

An alternative device embodiment is illustrated in FIG. 44. While theportion of the device that attaches onto the spinous process of theupper vertebral bone is largely identical to that of device 605, thecurrent embodiment contains two contoured rods 712 that are adapted toattach bone fasteners at multiple vertebral levels. In use, bodies 612attach onto the spinous process segment of an upper vertebral whilecontoured rod 712 attaches onto bone fasteners that are attached onto amiddle and a lower vertebral level. As before, the bone fasteners arepreferably, but not necessarily, anchored into the pedicle portion ofthe middle and lower vertebral bones. In this way, the currentembodiment provides a hybrid device that permits vertebral movementbetween a first and second vertebral bones and complete immobilization(and fusion) between a second and third vertebral bone. Clearly,additional fasteners can be attached to contoured rod 712 to immobilizeadditional vertebral levels. This device is particularly adapted for usewithin the lower lumber spine where it is frequently desirable toimmobilize and fuse the S1 and L5 vertebral levels and preserve motionbetween the L5 and L4 vertebral levels.

FIG. 45-48 show another embodiment of a device. The device includescentral members 4510 that are slidably attached to a rod 4515 thatextends through a bore 4513 in both of the central members 4510. Each ofthe central members 4510 has a u-shaped slot 4517 that is sized toreceive a contoured rod 115. As in the previous embodiments, the centralmembers are positioned on opposed sides of a spinous process and engagedthereto via spikes or barbs on the interior surface of the centralmembers.

A pair of locking nuts 125 are positioned within boreholes of centralmembers 4510 and adapted to produce a compressive force onto “C” ring119 and interconnecting rod 4515. A cross-sectional view of the lockingmechanism is illustrated in FIG. 48. As illustrated in priorembodiments, each ember 4510 can move relative to rod 115 in one or moreplanes while in the unlocked state. With actuation of locking nuts 125,members 4510 and rod 4515 are immobilized relative to one another. Rod115 is affixed to fasteners that are attached to the pedicle portion ofthe lower vertebral level. Rod is freely movable within slot 4517. Inuse, the device will preserve vertebral motion but prevent abnormaltranslational movement that produces spondylolisthesis.

FIG. 49 shows perspective views of an additional device embodiment whileFIG. 50 illustrates an exploded view. The present embodiment is similarto the preceding embodiment with the exception of placement of malleablemembers 131 between the interconnecting rod 4515 and rod 115. Themalleable member biases movement between the vertebral bones towards adefault position and resists vertebral movement away from that position.FIG. 51 illustrates an embodiment in which a cavity 242 is placed withineach spinous process abutment member in order to accept a bone formingsubstance. As noted in pervious embodiments, this feature would permitdevice fusion onto the spinous process of the first vertebral bone.Further, a bone graft or bone graft substitute 252 is positioned so thatrod 115 transverses a bore within member 252. This feature permits theestablishment of a bony fusion between rod 115 and the lamina or spinousprocess of the second vertebral bone.

Alternative device embodiments are shown in FIGS. 52 and 53. In eitherembodiment, the device is adopted to fixate three vertebral bones. Inthe embodiment of FIG. 52, the device anchors onto the spinous processof the middle vertebral level. Rod 890 is attached to bone fastenersthat are anchored into the pedicle portion of the lower vertebral level.Rod 890 is freely movable within slot 892 of the spinous processattachment member. Rod 902 is attached to bone fasteners that areanchored into the pedicle portion of the upper vertebral level. Rod 902is freely movable within slot 904 of the spinous process attachmentmember. In the embodiment of FIG. 53, rod 902 is freely movable withinslot 904 whereas arms 888 rigidly attach onto the spinous processattachment member using the same mechanism as that shown in FIG. 11. Inuse, the embodiment of FIG. 53 provides rigid fixation between themiddle and lower vertebral levels while permitting movement between theupper and middle vertebral levels.

A perspective view of an additional embodiment is illustrated in FIG.54. Multiple orthogonal views are shown in FIG. 55 while an explodedview is shown in FIG. 56. Interconnecting rod 2012 has articulationmember 2014 on each end. The spinous process engagement members and thelocking mechanism of the device are similar to prior embodiments, suchas that of FIG. 45. Rod 2022 is attached to bone fasteners anchored intothe pedicle portion of the lower vertebral bone. Rod 2022 has triangularprojections 2024 that articulate with articulation members 2014 of rod2012. The embodiment provides controlled movement between the twovertebral bones.

A perspective view of an additional embodiment is shown in FIG. 57.Exploded views are shown in FIG. 58 and a cross-sectional view throughthe articulation surface is illustrated in FIG. 59. While similar to theprior embodiment, this device employs a different articulationmechanism. Spherical members 2106 are contained at the end ofinterconnecting rod 2102. Two complimentary articulation surfaces 2112are attached to rod 2114. As shown in the cross-sectional view, thecomplimentary articulation surface 2112 contains a depression adapted toaccept spherical member 2106 and, preferably, the depression is largerspherical member 2106 so as to permit some additional translationalmovement. That is, the articulations form a “loose” joint.

FIG. 60A illustrates the posterior aspect of spine model whereas FIG.60B shows the placement of bone forming material between the lamina ofthe L4 and L5 bones. The bone forming material may be an actual bonegraft that is cut to the shape illustrated or a device adapted tocontain bone graft or bone graft substitute. FIGS. 61A and B showperspective and orthogonal views of an exemplary graft containmentdevice. As shown, the device preferably has a solid bottom that keepsthe contained bone forming material form impinging upon the nerveelements. The sides may be open or solid. The top is preferably open andcontains side protrusions 2302 that prevent anterior migration of thedevice into the spinal canal. An alternative device configuration isshown in FIG. 62. The latter device is intended to cross the vertebralmidline, whereas the former is placed on either side of the vertebralmidline.

The disclosed devices or any of their components can be made of anybiologically adaptable or compatible materials. Materials consideredacceptable for biological implantation are well known and include, butare not limited to, stainless steel, titanium, tantalum, shape memoryalloys, combination metallic alloys, various plastics, resins, ceramics,biologically absorbable materials and the like. Any components may bealso coated/made with osteo-conductive (such as deminerized bone matrix,hydroxyapatite, and the like) and/or osteo-inductive (such asTransforming Growth Factor “TGF-B,” Platelet-Derived Growth Factor“PDGF,” Bone-Morphogenic Protein “BMP,” and the like) bio-activematerials that promote bone formation. Further, any surface may be madewith a porous ingrowth surface (such as titanium wire mesh,plasma-sprayed titanium, tantalum, porous CoCr, and the like), providedwith a bioactive coating, made using tantalum, and/or helical rosettecarbon nanotubes (or other nanotube-based materials) in order to promotebone in-growth or establish a mineralized connection between the boneand the implant, and reduce the likelihood of implant loosening. Lastly,the system or any of its components can also be entirely or partiallymade of a shape memory material or other deformable material.

Although embodiments of various methods and devices are described hereinin detail with reference to certain versions, it should be appreciatedthat other versions, embodiments, methods of use, and combinationsthereof are also possible. At a minimum, any feature illustrates in onedevice embodiment may be alternatively incorporated within any otherdevice embodiment. Therefore the spirit and scope of the appended claimsshould not be strictly limited to the description of the embodimentscontained herein.

What is claimed:
 1. An orthopedic assembly, comprising: a central memberhaving a central threaded bore, a footplate, and a pair of fixation rodsupports with a threaded recess; a pair of moveably attached fasteningrods with spherical heads, the fastening rods extending outwardly from apair of cavities in the central member; a fixation rod adjustablycoupled to the fixation rod supports of the central member; and a pairof threaded fixation rod locknuts complementary to the threaded recessof the fixation rod supports, wherein the fixation rod locknuts securethe fixation rod in a fixed relationship with the central memberfixation rod supports.
 2. The assembly of claim 1, further comprising apair of collapsible c-rings configured to encircle the spherical head ofeach fastening rod and secure it within the cavity in the centralmember.
 3. The assembly of claim 1, further comprising a pair of bonefasteners and fastener lock nuts, each bone fastener having arod-receiving seat.
 4. The assembly of claim 3, wherein the fastenerlock nuts secure the fastening rods in the rod-receiving seat of thebone fasteners such that the fastener rods are immobilized relative tothe fasteners.
 5. The assembly of claim 1, further comprising a pair oflocking plugs, wherein engagement of the fixation rod locknuts advancesthe locking plugs onto the spherical heads of the attachment rodsimmobilizing them relative to the central member.
 6. The assembly ofclaim 1, wherein the fixation rod is u-shaped, and wherein both ends ofthe u-shaped rod are connected to the rod supports of the central memberand immobilized by engagement of the threaded locknuts in the threadedrecess.
 7. The assembly of claim 1, wherein the fixation rod comprises afirst rod component and a second rod component, each with a supportengagement end and a hook end.
 8. The assembly of claim 7 wherein thesupport engagement end of the first and second components are connectedto the rod supports of the central member and immobilized by engagementof the locknuts in the threaded recess.
 9. The assembly of claim 8,wherein the hook ends of the first and second rod components attach tothe spinous process of a vertebral bone.
 10. The assembly of claim 8,wherein of the hook end of the first rod interconnects with the hook endof the second rod to form a u-shaped rod.